A serious drawback in traditional faucets is that they are easily contaminated with germs. The germs can then be transferred from one person using the faucet to the next person using the faucet when each person has touched the handle of the faucet. Many users fear contacting the germs by touching the faucet handle. This fear prevents many users from using faucets in public. A hands-free faucet, on the other hand, eliminates the problem of users contacting germs and the fear of using faucets in public.
In many hands-free faucets, a sensor detects the presence of the user. Many of the sensors use infrared light. In order to sense the user with these units, the user must be located directly in the path of the light beam. Accordingly, if the user does not stand directly in that light path, or moves out of the light path, then the sensor does not detect the user, and the water will not turn on or will turn off before it should. One way to overcome this shortcoming in a hands-free faucet is to utilize a capacitive field sensor. This type of sensor, which works by detecting an electric charge at or near the sensor, can detect the presence of a user whenever he or she is near the faucet. A faucet using a capacitive field sensor is designed to remain activated as long as the user is near the faucet.
Automatic faucets using capacitive field sensors, however, have been found to have several significant problems. First, faucets have turned on for no apparent reason. This appears to have occurred when there is some movement near the faucet, even if not by an approaching user. Such movement can be a nearby faucet turning on, a nearby toilet flushing, or someone walking by the unit. Second, these faucets have not always worked consistently and, at times, would not stay on as long as they should. This appears to have occurred when the sensor switches its operational mode from sensing a user through the air surrounding the sensor, to sensing the continued presence of the user through the flow of water.
The present invention solves these problems in hands-free faucets that use capacitive field sensors. It is desirable, in particular, to have a hands-free faucet that uses a capacitive field sensor and that will turn on only when approached by the person desiring to use the faucet. It is also desirable to have a hands-free faucet that uses a capacitive field sensor in which the faucet will continuously be on, without shutting off prematurely, the whole time that the user is near the faucet and desiring to wash his or her hands.